The invention relates to a lighting device with a light source and a first reflector which guides light originating from the light source to at least two focal points when in the operational state, as well as to a method of operating such a lighting device.
Such lighting devices and methods are known, for example, from EP 0 501 669 B1. They usually serve to split up the light originating from a light source into two or more beams, in particular for the purpose of feeding them into optical fibers. It is possible thereby to operate, for example, two motor vehicle headlamps which will then radiate light of exactly the same color and substantially the same intensity.
It is often necessary, however, in such lighting devices to xe2x80x9cswitch offxe2x80x9d one of the light beams. This has been achieved by means of covering diaphragms until now, which close, for example, the emission opening of an optical fiber.
The use of diaphragms, however, requires that the diaphragm or the associated lighting device should be capable of absorbing the obstructed light, which often leads to thermal problems because of the fact that often high-intensity light sources are used in lighting devices of the kind described here.
Accordingly, the invention has for its object to provide a lighting device and a method of operating a lighting device of the kinds mentioned in the opening paragraph which render it possible to xe2x80x9cswitch offxe2x80x9d a light source upon demand without the light which is not required leading to thermal problems.
This object is achieved by means of a device with the characteristics of claim 1 and a method with the characteristics of claim 9. Advantageous embodiments and modifications are defined in the dependent claims.
The invention thus presents a lighting device of the type indicated which comprises at least a second reflector. This reflector is designed such that it is capable of diverting away the light which was guided to a first of the two focal points by the first reflector at least partly towards the second one of the two focal points, if so desired. This diversion may take place directly or indirectly.
The invention thus provides a method of the type indicated by which the light guided to the first of the two focal points is directly or indirectly, as desired, diverted at least partly to the second one of the two focal points.
Such a device is of a particularly simple construction, and such a method is particularly easy to implement, when the second reflector is a mirror which can be displaced or pivoted into the radiation path of the light from the light source to the first focal point, or can be rotated into this radiation path. Alternatively, the second reflector may be an electronic mirror, or a mirror whose mirroring properties can be changed in some other way, which is preferably positioned in the radiation path of the light from the light source to the first focal point, which mirror can be switched over between a reflection and a transmission operation. It then suffices for switching on and off merely to operate the mirror in the corresponding manner, i.e. to displace, pivot, rotate, or switch over the mirror.
Means for transmitting the radiation further may be provided in the two focal points. Preferably, light input openings of light waveguides or optical fibers are provided in or adjacent the two focal points. It is particularly easy in this manner to pass on the light beam divided by the radiation divider of the lighting device to desired locations. It is obvious that alternative radiation paths such as, for example, mirror arrangements or optical systems may be provided before the light is fed into a light waveguide or an optical fiber.
Preferably, the second reflector is constructed such that it prevents at least substantially the input of light into one of the light input openings, in particular into the light input opening arranged at the first focal point, in the case of the optional diversion of light.
A further transmission of light from the first focal point can be prevented in a particularly simple manner thereby.
The entire arrangement has a particularly simple construction if the first reflector is comprised of two half ellipsoids, each with two focal points, said half ellipsoids being arranged such that they have one focal point in common, in which the light source is positioned.
If the second reflector is positioned in the geometric center of one of the two half ellipsoids in the case of the optional light diversion, substantially all light will be guided back into the common focal point and thus entirely into the second focal point belonging to the second half ellipsoid. It is similarly possible to arrange the second reflector in or adjacent the first focal point in the case of the optional light diversion. In this case, however, the reflector cannot be introduced simply rectilinearly, as in the alternative mentioned above, but should be exactly adjusted. In particular, a non-planar reflector shape may alternatively be used for the second reflector. It was surprisingly found in practice that the latter alternative has a better light efficiency than the former alternative, which is theoretically superior.
It is obvious that more than two focal points can be provided with light from the one light source, provided the first reflector has a suitable construction. It is also possible in particular to install several reflectors which correspond to the second reflector and which are each associated with the various focal points.
The invention has the major advantage that the light not required in a certain location is not converted into useless heat, but instead is at least partly directly or indirectly guided to one or several other focal points, in particular by means of reflection at the first reflector, in which other focal points it enters, for example, optical fibers and can be used for enhancing the luminous intensity.